1. Field of the Invention
The present invention relates to the field of electrical machines. It relates to a connection arrangement for the stator winding of a turbo machine with two or more parallel circuits.
2. Brief Description of the Related Art
There are numerous schemes in which the connections are led from the stator winding of an electrical machine to the machine or generator housing in order to be connected there to the busbars. In general, the connecting conductors are in this case led from the phase connection location, i.e., from the ends of the winding bars protruding out of the slots of the stator body, along the rear side of the evolute of the stator end winding up to external connections arranged on a circumferential circle.
The arrangement used depends on the winding scheme, in particular on the number of phases, the number of poles and the number of circuits per phase. In general, the various phase connecting conductors are arranged such that the sum of the currents of all phase rings at any desired circumferential location is limited to a specific value in order to avoid imbalances in the magnetomotive force (MMF) resulting from the currents in the phase rings. In general, such connecting rings (phase rings) are insulated individually and laid individually according to the physical and electrical boundary conditions.
The article by Nagano S, Kitajima T, Yoshida K, Kazao Y, Murata D, Nagakura K., “Development of world's largest hydrogen-cooled turbine generator”, PES Summer Meeting July 2002, Proceedings volume 2, pages 657-663 describes the construction and testing of a hydrogen-cooled 500-600 MVA generator. FIG. 15(b) therein illustrates the phase ring connections and shows that the winding has three phases, of which each has three parallel circuits, all six external connections being arranged on the base of the machine. The three parallel circuits are arranged such that they run together in adjacent stator slots within a phase group. However, the phase rings which connect them to the external connections are insulated individually and led individually to a suitable external connection.
The article by R. Lari and V. Tartaglione, “THR-L63, An Advanced Generator coupled front and back to gas and steam turbine for single shaft configuration”, PowerGen Europe, Dusseldorf 6-8 May 2003, describes the construction of a hydrogen-cooled 400 MW generator. The diagram shown therein on page 11 of the end winding supports shows that the winding likewise has three phases, which each have three parallel circuits, and three external connections on the base and three external connections on the upper side of the machine. The three parallel circuits are arranged such that they run together in adjacent slots of the stator within a phase group. However, here too, the phase rings which they connect to the external connections are insulated individually and led individually to a suitable external connection.
The known technique of individually leading the phase ring connections means that each ring needs to be insulated from the full voltage between two phases and mounted and installed individually. This results in impaired thermal properties of the connecting conductors and an increased space requirement owing to the thicker bar insulation and/or owing to the increased distance between the bars. Also, the need to manufacture and install individual bars results in the manufacture and assembly of the winding being time-consuming and expensive. This is particularly the case when each phase has more than two parallel circuits.